Probing pulsar winds using inverse Compton scattering

We investigate the effects of inverse Compton scattering by electrons and p ositrons in the unshocked winds of rotationally-powered binary pulsars. Thi s process can scatter low energy target photons to produce gamma rays with energies from MeV to TeV. The binary radio pulsars PSR B1259 - 63 and PSR J 0045 - 73 are both in close eccentric orbits around bright main sequence st ars which provide a huge density of low energy target photons. The inverse Compton scattering process transfers momentum from the pulsar wind to the s cattered photons, and therefore provides a drag which tends to decelerate t he pulsar wind. We present detailed calculations of the dynamics of a pulsa r wind which is undergoing inverse Compton scattering, showing that the dec eleration of the wind of PSR B1259 - 63 due to 'inverse Compton drag' is sm all, but that this process may confine the wind of PSR J0045 - 73 before it attains pressure balance with the outflow of its companion star. We calcul ate the spectra and light curves of the resulting inverse Compton emission from PSR B1259 - 63 and show that if the size of the pulsar wind nebula is comparable to the binary separation, then the gamma-ray emission from the u nshocked wind may be detectable by atmospheric Cherenkov detectors or by th e new generation of satellite-borne gamma-ray detectors such as INTEGRAL an d GLAST. This mechanism may therefore provide a direct probe of the freely- expanding regions of pulsar winds, previously thought to be invisible. (C) 2000 Elsevier Science B.V. All rights reserved. PACS. 95.30.Jx: 95.55.Ka; 9 7.60.Gb; 98.70.Rz.